If your work involves drawing plans and supervising them, then it is permissible work so long as you do not draw plans for buildings that will be used for evil purposes, such as riba-based banks, bars, gambling halls and other places that are used for sinful and immoral purposes, because in that case drawing plans would come under the heading of helping in sin and increasing the numbers of buildings used for evil. See question no. 82551.
As for drawing plans for permissible buildings, such as houses in which people will live, there is nothing wrong with that, even if the owner is going to build them with money that he has borrowed with riba, because you are not helping him in his sin – which is borrowing money with riba – rather you are doing permissible work for him and being paid for it.
Among the companions of the Prophet (peace and blessings of Allaah be upon him) were some who did work for pay for some of the Jews, doing permissible jobs such as watering crops and so on. It is known that most of the Jews engage in riba and consume people’s wealth unlawfully, as Allaah says (interpretation of the meaning):
“For the wrongdoing of the Jews, We made unlawful for them certain good foods which had been lawful for them — and for their hindering many from Allaah’s Way;
161. And their taking of Riba (usury) though they were forbidden from taking it and their devouring of men’s substance wrongfully (bribery). And We have prepared for the disbelievers among them a painful torment”
The Prophet himself (peace and blessings of Allaah be upon him) dealt with the Jews, buying and selling, and when the Messenger of Allaah (peace and blessings of Allaah be upon him) died, his shield was in pledge to a Jew for some foodstuff that he had bought from him. Narrated by al-Bukhaari (2916).
Hence it is known that it is permissible to sell cement, sand and gravel to a person who is going to use them to build permissible buildings, even if the owner is one of those who engage in riba.
We appreciate your keenness to find out what is halaal.
We ask Allaah to suffice us with that which is halaal so that you will have no need of that which is haraam, and to make us independent of means by His bounty.
And Allaah knows best.